I mean, maybe I'm looking at it wrong, but I think all of those bolts are in single shear, which is a total no-no for any sort of suspension part. And the loadings those bolts would experience just look all wrong to me. (The bolts/nuts are going to be under tension and compression, and generally you want your suspension bolts to be under double shear force.)
A better adapter would have the bolts going "left-right" instead of "up-down," if that makes sense.
In reply to Sky_Render:
That makes sense. Im toying with the idea of either extending an s13 arm to get the right length or going tubular (full custom)
Because this is a strut car the forces on the lower control arm are predominantly horizontal so the plate doesn't have to be terribly thick but it's imperative that you're not relying on just the clamping force to prevent horizontal movement. In this case, with that part designed as is, the bolts need to be a tight fit in the holes and the parts of the bolts in the the holes need to be un-threaded. An alternative would be to use pins to do the locating and use the bolts just for clamping. Do you have any other pictures? I'd like to see what the control arm looks like in that area and how the ball joint is attached to the adapter plate.
Second look:
I'm used to double a-arm cars (in which case that plate would carry the weight of the car), but I forgot these are McStruts, so it doesn't. In that case I think you're just fine. I would generally agree with APE that making the bolt holes tight is a good idea.
In reply to APEowner:
The ball joint is bolted to the underside of the plate. Would welding it in be beneficial?
Update: rear suspension arms have been bought and wheels are on the way. Pics when they arrive 
Wheels arrived yesterday 
Should look good on the car. Just gotta finish the suspension first 
Nice, who makes the wheels?
In reply to PseudoSport:
Atara Racing
These are 17x9
Stock rear end is now out of the car:
Began measuring everything up.
Based on so quick calculations the front mounts on the s13 subframe need to come inboard by 0.9375" each. Im guessing cut and weld is probably the best solution for this but Im open to suggestions.
This build has not been forgotten! Been working on the balljoint adapter plate design and messing with the ae86 we bought.
Pic of the adapter being designed:
First prototype:
Thank god my girlfriend can do solidworks
Got the prototype 3d printed and then ground down to test fit in the control arms. Now to fix the model and have another one printed to make sure the measurements are right.
Finally set a deadline for this stupid project. Want to have it drive-able enough to make it to Zcon 2018. Because of this goal, I bought a parts S13 to take the subframe and subframe mounts from. Should make this go a bit faster.
Pic of the new (but still old) subframe:
Still need to finalize the material and design for the front adapter as well. Currently thinking about a single plate on top of the arm that is 10mm thick and mild steel. Any ideas if that will hold?
Stock RX7 ball joints are arranged in a similar fashion and only have 2 bolts that hold it.
Fitzauto said:Finally set a deadline for this stupid project. Want to have it drive-able enough to make it to Zcon 2018.
I'm going to try and make it in my 240 to the 2018 event. I know a lot of the Atlanta Z people and that's where my z still hibernates. I may just see you there.
Thats a pretty big hole in the S13
BAM! Rear mounts have now left the S13 and are ready to be cleaned up and welded into the 280zx.
Googling Atara wheels 17 x 9 +35 please!
Sadly they have yet to release a one piece wheel that is positive offset. The 3 piece can be whatever you want though!
Text update since it has been awhile:
Rear crossmember is almost ready to come out of the Z
A new engine has been sourced (adding 2 cylinders)
The rest of the build from this point on will be documented on my youtube channel in an effort to build up a following for my business.
Hope you all will still follow along!
First video of Z work is up!
You can watch it here: https://youtu.be/Jg21tz_-3PY
Please Subscribe if you wanna follow my automotive shenanigans.
Finally got the rear mount welded in and the subframe sorta in.
However, it may be crooked. It measures out straight but the driver wheel is one index finger with further back that the passenger side. Sould it be an alignment thing or subframe twisted?
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